In 1904, Schardinger first characterized cyclodextrins as cyclic oligosaccharides. The .alpha., .beta., and .gamma.-cyclodextrins, which consist of six, seven, and eight glucose units, respectively, are the most common natural cyclodextrins.
Cyclodextrins have been used as inclusion complexes by complexing with a guest compound or molecule as a host compound or molecule. Such inclusion complexes have been used to mask the bitter taste or unpleasant odor of a guest compound, to solubilize a hardly soluble guest compound, to enlarge the stability of a guest compound against heat, light, or air, to stabilize emulsions, or as a sustained release preparation using a hydrophobic alkylated cyclodextrin. See U.S. Pat. No. 4,869,904. However, no one has attempted to make carboxyacylated cyclodextrins, or used such cyclodextrin derivatives to form ionic sustained release compositions.